I have two NEC MultiSync LCD 2070NX monitors connected (DVI) to a Dell Precision T5500 workstation with Windows 7 Professional. One monitor does not work properly. The screen is black, showing no picture. Remote CONTROLLING the computer, I can use both screens as if everything was OK.

Tested the monitor on another computer having Windows 10 Professional, similar hardware, and now connected with VGA, the same problem occurs. Everything is working fine remotely, as if there were two screens with no problems while remote controlling the computer. The monitor itself does not have any pictures, no display, and the screen stays black. A green lamp shows that the monitor is switched on.

Is the monitor broken? Can I somehow repair or fix this problem before THROWING it?
Some Dell displays require you to use the built-in setup to identify the connection you are using. Use the button on the display itself to enter the menu and choose the vga connection. If that doesn't work, try a different type of connection or cable.The monitor does not show any response when using the buttons. Stays black.I have tested the monitor on one computer, connected to DVI and on another computer, connected with VGA. Same result. Different computers. Different cable connections.Is it a new display?
No. It is several years old.Vid card...or onboard ? ?NVIDIA Quadro FX 580 Cards on both computers used for testing.
Then double-check all settings in nVidia Control Panel...Other similar monitors are connected to both computers used for this testing, and working. The problem cannot be on the computer side, as far as I can tell. The problem is one of several equal monitors.Then don't check the settings...not sure why your convinced it's not on the PC's end...I am not sure where the problem sits. However, having other similar monitors connected to both the first test machine and the second test machine, and all working well except one gives me a hint of the problem being the monitor. Also testing both computers while using both the DVI and the VGA connections. All working well except this specific monitor.

I have now OPENED the NVIDIA Control Panel. It is in NORWEGIAN, but I will try to follow your advice.